Spark plug



June 28, 1938. E, E, BIDWELL 2,122,242

SPARK PLUG I Filed Aug. 26. 1957' v f' zz/erzzr flu"! Z15 idwez PatenteJune 28, 1938 lTE AT SPK PLUG Earl E. Bidwell, Gary; lind., assignor toProductive Inventions, Inc., Gary, Ind, a corporation of IndianaApplication August 26, 1937, Serial No. 161,098

28 Claims.

This invention relates to spark plugs constituting a part of theignition systems of internal combustion engines or motors, and moreparticvide a novel construction and arrangement in.

spark plugs whereby the character and position of the spark isautomatically determined by the operating conditions of the engine, inconnection with which my improved plug is employed.

Another object of the invention is to provide -a novel construction andarrangementwhereby the life or length of service of the plug ismaterially increased, and wherein the necessity of frequent cleaning andadjustment of the points thereof is obviated.

Another object of the invention is to provide a spark plug of improveddesign wherein the position of the spark will materially facilitatestarting of a cold motor, for example, and wherein the spark willautomatically shift to a position to provide the most efficientoperating conditions after the motor has warmed up.

A further object of the invention is to provide a spark plug of novelconstruction contributing to the efiicient operation of a motor atidling speeds, and the maintenance of the points of the plug in a cleancondition to insure eflicient operation thereof.

A still further object of the invention is to improve devices of thecharacter described in sundry details hereinafter referred to andparticularly pointed out in the appended claims.

One embodiment of the present invention is I shown for illustrativepurposes in the accompanying drawing, in which:

Fig. 1 is a vertical sectional elevational view of a spark plugembodying features of the present invention, and taken substantially asindicated by the line l-l of Fig. 2; and

V Fig. 2 is a bottom plan view of the spark plug illustrated in Fig. 1.

In approaching the subject of the present ap- I sufficiently shortlength to insure proper starting and cold-motor performance, there beingno provision, however, for increasing the gap as the motor warms up toprovide a longer spark found to be more effective under hot motorconditions, which exist at higher speeds and under higher compression.

As illustrated in the acompanying drawing, the present inventioncomprises a shell indicated, as a whole, by the numeral 3, and mountedtherein is a core indicated, as a'whole, by the numeral t formed ofsuitable insulating material such, for example, as porcelain or thelike, the core t being secured in position within the shell 3 by meansof a gland 5 screw threaded into a portion of the shell, as indicated at6.

In the type of plug shown in the drawing, the shell 3 is provided withan elongated chamber 1 having cylindrical side Walls 8 inclined towardeach other and terminating adjacent their lower ends in a relativelythin transverse wall portion 9 having an opening I l formed therein,preferably, of substantially less diameter than the diameter of thechamber 1 to provide a restricted opening communicating with theinterior of the chamber adjacent the end of the plug, it beingunderstood that in the type of plug shown, and under normal operatingconditions, a charge of combustible mixture in the chamber 1 is ignited,thereby projecting a constricted jet of flame through the opening II forigniting the main charge of combustible mixture in the combustionchamber of the engine.

It will be observed by reference to Fig. 1 that the lower end portion l2of the core t extends a substantial distance into the chamber 1 towardthe opening H, and mounted within the core, is a central electrode l3adapted to extend beyond the end portion .12 of the core, through aportion of the chamber 1 and preferably, into or through a portion ofthe opening H at the end, of the shell 3.

Mounted on the shell 3, preferably, on'the lower end portion thereof andadapted to extend across a substantial portion of the end wall 9 is aground electrode indicated, as a whole, by the numeral I4, provided withan inwardly extending. portion l5 positioned within the opening II andextending a substantial distance into the chamber 1 to adjacent theinner end portion l2 of the core 4, and into overlapping relationshipwith the central electrode 13, the portion I5 of the ground electrode I4 being inclined with respect to the central electrode l3 in a manner toposition the adjacent side portions of the respective electrodes ininclined relation with respect to each other to provide a tapered sparkgap within said chamber 7, the said gap having its narrowest portionadjacent or within the opening I I, and its widest portion adjacent theend I2 of the core 6. By such an arrangement, it will be observed thatthe narrowest portion of the gap is positioned adjacent the end of theshell to provide a gap of sufliciently short width closely adjacent thecombustion chamber of the engine to provide a suitable spark for idlingspeeds and to facilitate easy starting of a cold motor.

When a motor is cold, there is practically no diiference in thetemperature and density. of the mixture throughout the levels occurringbetween the lower end and the upper end of the spark gap formed betweenthe electrodes I3 and portion I5 of the ground electrode, and under suchconditions, the spark occurs at the shorter distance across the lowerend of the gap adjacent the top of the compression or combustion chamberof the cylinder, so that direct exposure of the spark to the mixture inthe compression chamber is assured to provide greater certainty ofmaximum efiiciency in starting, and under cold-motor conditions, thus,it will be apparent that, for the purpose of reducing resistance andinsuring a competent, efficient spark, the spark gap under cold motorconditions should be comparatively short.

As the motor temperatures increase, however, and the plug becomes hot,as when the motor is operating under conditions of higher speeds, awider spark gap for providing a longer spark is desirable, and undersuch conditions, the porcelain, for example, adjacent the lower end ofthe core 3 and the chamber 1 becomes more heated, and the mixture withinthe chamber I, particularly adjacent the core, becomes rarified ascompared with the relatively cooler mixture at the ceiling or top of thecombustion chamber, thus, comparatively, reducing the resistance to thepassage of a spark between the electrodes adjacent the core and causingthe spark to move to a higher level within the chamber I or closer to apoint adjacent the upper end of the portion I5 of the ground electrodeIt. It will be observed that the rarification of the mixture producedadjacent the heated portion I2 of the core 4, and adjacent the widestportion of the spark gap, provides an area of low resistance adjacentthe upper inner end of' the portion I5 and provides a longer spark wellwithin the chamber I to insure complete combustion of the mixturetherein, particularly when the engine is operating at high speeds and athigh temperatures.

In other words, it will be readily understood from the conventionalconstructions of internal combustion engines and conventional methods ofoperating such engines, that when the piston approaches that end of thecylinder which carries the spark plug in the act of compressing anexplosive charge, the interval of time between the beginning of suchstroke and the instant at which said spark occurs is extremely shortexcept when said engine is being actuated slowly by the starter or isoperating at relatively low speed before attaining relatively highspeed. Due to the relative shortness of this interval when the motor isoperating at high speeds, and to the constricted opening II in the endof the plug.

there is not then sufficient time for the charge .of fuel to fullyequalize its compression as between the cylinder proper and the chamberof the Bidwell plug. It is apparent therefore, that this high speedcondition produces at the instant of the spark, at points well withinthe chamber of the Bidwell plug, a lower compression of fuel than isproduced adjacent the cylinder and adjacent the open end of saidchamber. Thus the gas between the inner end of the electrode I5 and thatportion of electrode I3 which is transversely opposed thereto is of lessdensity than the gas between the outer end of electrode I3 and thatportion of the electrode l5 which is transversely opposed thereto. It isthus seen that this compression difierential cooperates with thetemperature differential, elsewhere herein referred to, to produce atthe wider portion of said tapered spark gap a more rarifled gasandtherefore less resistance to the spark than under conditions existingcoincidentally at the shorter portion of said gap.

' Thus the spark occurs adjacent the opening of the chamber whenstarting and when operating at relatively low speed and when the motortemperature is relatively lowand occurs substantially within saidchamber when operating at relatively high speed and when the motortemperature is relatively high-the terms motor and engine as used hereinbeing synonymous.

An arrangement of the character described, which has been found to bevery efflcient and desirable is one wherein the spark gap adjacent thelower end of the central electrode I3 is approximately .030 of an inch,the adjacent side portions of the respective electrodes diverginginwardly of the chamber or toward the end of the insulating core toprovide a gap adjacent the upper or inner end of the portion I5 ofapproximately .037 of an inch, it being understood, however, that thesedimensions are merely relative and illustrative, and that the dimensionsmay be varied to suit conditions under which the improved spark plug isemployed.

It will be observed from the foregoing description that a suitable gapof reduced dimensions is provided adjacent the opening in the lower endof the plug to insure efiicient starting of a cold motor, and that asthe temperature increases the spark moves upwardly along adjacent sideportions of the electrodes in accordance with the operating conditionsof the engine, this upward movement being induced by the greaterrarification and lower resistance of the mixture adjacent the endportion I2 of the core I, the spark being maintained at the higher levelin the chamber I under hot motor conditions due to the relativedifference in temperatures at the opening II and at the upper orinnerend of the portion I5, the relatively cool incoming mixtureentering the combustion chamber of the engine tending to maintain alower temperature adjacent the opening II, while the heat retained inthe chamber 1, and particularly by and adjacent the lower end portion I2of the core 4, serves to maintain a relatively higher temperatureadjacent the upper end of the portion I5 or at the wider gap between theelectrodes, thereby producing a most emcient spark well within thechamber I to insure eflicient combustion of the charge therein and, byreason of the jet of flame therefrom, insuring more complete ignition ofthe charge within the combustion chamber of the engine.

It will be observed also, that by reason of the shifting of the sparklongitudinally of the electrodes, no one portion of the respectiveelectrodes is subjected to a burning away action caused by continuoussparking heats at one point only, as in conventional types of plugs and,as a consequence, whatever burning away of the electrodes, as may occur,is distributed throughout isease the length of the electrodes over whichthe spark automatically shifts, so that the rate of reduction of thecross section of the respective electrodes is materially reduced, andnecessity for frequent adjusting of the spark gap is thereby avoided,thus materially increasing the life or length of service of a plugembodying features of the present invention, and by reason of thescavenging action of the plug in projecting a jet of flame from thechamber 1, the necessity of frequent cleaning of the plug is obviated.

Obviously, the present invention is not limited to the preciseconstruction and arrangement shown and described; as the same maybevariously modified without departing from the spirit and scope :of theinvention as set forth in the appended claims.

What I claim as new Letters Patent is:

1. A spark plug comprising a shell having a chamber formed thereinadjacent one end thereof and having an opening communicating with saidchamber, an insulating core mounted in said shell, an electrode mountedin said core and extending beyond the end thereof and into said chamber,and a second free-ended electrode mounted on said shell and having itsfree end and desire to secureby extending into said chamber toward saidcore and into overlapping unilateral spaced relationship with saidfirst-mentioned electrode, adjacent portions of the respectiveelectrodes being inclined within said chamber with respect to each otherand diverging toward said core.

2. A spark plug comprising a shell having a chamber formed thereinadjacent one end portion thereof and having a constricted opening insaid end portion communicating with said chamber, an insulating coremounted in said shell, a wire-like electrode mounted in said core andextending beyond the end thereof to adjacent said opening, and a secondwire-litre electrode mounted on said shell and having a free andextending into said chamber toward said core and into overlappingspark-gap relationship with said first-mentioned electrode, adjacentportions of the respective electrodes being inclined with respect toeach other and diverging from adjacent said opening toward said core.

3. A spark plug comprising a shell having a chamber formed thereinadjacent one end portion thereof and having an opening in said endportion communicating with said chamber, an

' insulating core mounted in said shell, an electrode mounted in saidcore and extending beyond the end thereof through a portion of saidcham=her to adjacent said opening, and a second elec-. trode mounted on saidshell adjoining said opening and extending through said opening and intosaid chamber and into overlapping relationship in said chamber with saidfirst-mentioned electrode, adjacent portions oi the respectiveelectrodes being inclined with respect to each other and divergingwithin said chamber irom adja cent said opening toward said core.

l. A spark plug comprising a shell having a chamber formed thereinadjacent one end portion thereof and having an opening in said endportion communicating with said chamber, an insulating core mounted insaid shell and extending into said chamber, a wire-like electrodemounted in said core and extending beyond the end thereof through aportion of said chamber and substantially coaxially therewith toadjacent said opening, and a second wire lilre electrode mountedexternally of the end portion of said shell and extending through saidopening into said chamber and into unilateral overlapping non-parallelspaced spark gap relationship within said chamber with saidfirst-mentioned electrode, adjacent side portions of the respectiveelectrodes being inclined with respect to each other and diverging fromadjacent said opening toward said core and the interior of said chamber.a

5. A spark plug comprising a shell having a chamber formed thereinadjacent one end portion thereof and having an opening in said endportion of less diameter than the diameter of said chamber andcommunicating therewith, an insulating core mounted in said shell andextending a substantial distance into said chamber in spaced relation tothe side walls thereof, an electrode mounted in said core and extendingbeyond the end thereof through a portion of said chamber and into saidopening, and asecond electrode having one end mounted on the end portionof said shell and its free end extending through said opening into saidchamber into a free position adjacent said core and into operative sparkgap relationship with said first-mentioned electrode, adjacent sideportions of the respective electrodes being inclined with respect toeach other and diverging from within said opening toward said core andthe interior of said chamber.

6nd sparlsplug comprising a shell having a chamber formed therein, saidshell having a transverse wall portion adjacent one of its endsproviding an end wall for said chamber, said end wall having an openingtherein of substantially less diameter than the. diameter of saidchamber. an insulating core mounted in said shell and extending asubstantial distance into said chamber, a central electrode mounted insaid core and extending beyond the end thereof to adjacent said opening.and a ground electrode mounted on said shell and extending into saidchamber to adjacent said core and in overlapping relationship with saidcentral electrode, adjacent side portions of the respective electrodesbeing inclined with respect to each other and providing a tapered sparkgap within said chamber, said gap having its narrowest portion adjacentsaid opening and its widest portion ad jacent said core.

7. A sparlr plug comprising a shell having an elongated chamber formedtherein, said shell having a relatively thin transverse wall portion ad=jacent one of its ends providing an end wall for said chamber, said endwall having an opening therein of substantially less diameter thanthediameter of said chamber, an insulating core mounted in said shell andextending a substantial distance into said chamber, a central electrodemounted in said core and extending beyond the end thereof and into saidopening, and a ground electrode mounted on said wall and extending fromsaid wall into said chamber to adjacent the inner end of said core andin overlapping relationship with saidcentral electrode, adjacent sideportions of the respective electrodes being inclined with respect toeach other to provide therebetween a tapered spark gap within saidchamber, said gap having it nar w st p0r= tion adjacent said opening andits widest portion adjacent said core.

i her, said end wall having an ope ningtherein of substantially lessdiameter than the diameter of said chamber, an insulating core mountedin said shell and extending a substantial distance into said chamber, acentral electrode mounted in said core and extending beyond the endthereof and into said opening, and. a substantially L- shaped groundelectrode having one of its legs .mounted on the end portion of saidshell and extending across a substantial portion of said end wall andhaving its other leg extending freely into said chamber to adjacent theinner end of said core and in overlapping spaced relationship with saidcentral electrode, adjacent side portions of the respective electrodesbeing inclined with respect to each other to provide a tapered spark gapwithin said chamber, said gap having its narrowest portion adjacent saidopening and its widest portion adjacent said inner end of the core.

9. A spark plug comprising a shell having a chamber formed thereinandproviding side walls for said chamber, the inner surface of said sidewalls being inclined toward each other and terminating at their lowerends in a transverse wall portion adjacent one end of said shell andproviding an end wall for said chamber of substantially lesser thicknessthan the thickness of said side walls, said endwall having an openingtherein of substantially less diameter than the diameter of saidchamber, an insulating core mounted in said shell and extending asubstantial distance into said chamber, a central electrode mounted insaid core and extending beyond the end thereof to adjacent said opening,and a substantially L-shaped ground electrode having one of its legsmounted externally on the end portion of said shell and extending acrossa substantial portion of said end-wall andhaving the other of its legsextending freely into said chamber to adjacent the inner end of saidcore and in overlapping spaced relationship with said central electrode,adjacent side portions of the respective electrodes being inclined withrespect to each other to provide a tapered spark gap positioned in partwithin said chamber, said gap having its narrowest portion adjacent saidopening and its widest portion' within said chamber and adjacent saidcore.

10. In a spark plug of the kind described and in combination, a shellhaving a chamber formed adjacent one end thereof and provided with awall forming the end wall of said chamber, said wall having an openingthrough the same of a diameter substantially less than the diameter ofsaid chamber, a core of insulating material, mounted in the shell andprojecting into the chamber, an electrode extending through said coreand projecting into the chamber to adjacent the opening in said endwall, a second electrode mounted on the shell and having its free endprojecting into said chamber toward the inner end of said core, the axisof said second electrode diverging from the axis of said first 1 1. In aspark plug of the kind described and in combination, a shell providedwith a chamher at the inner end thereof, the end of the shellconstituting an end wall of the chamber and provided with an openingthrough the same, a core of insulating material mounted in said shellwith a portion of said core constituting a I,

portion of the inner wall of said chamber, an insulated electrodecarried by said core and projecting into said chamber with its free endpositioned adjacent said opening, a second electrode mounted on saidshell and having a portion intermediate its ends positioned adjacent thefree' .end of said insulated electrode and projecting inwardly with thefree end of said second electrode positioned-adjacent the core end andspaced a greater distance from said insulated electrode than thedistance between the free end of said insulated electrode and theadjacent intermediate portionof said second electrode to provide atapered spark gap within said chamber.

12. A spark plug comprising a shell having a recess formed thereinadjacent one end thereof and having an opening communicating with saidrecess, an insulating core mounted in said shell, an electrode mountedin said core and extending beyond the end thereof and into said recess,and a second electrode secured to said shell adjacent said opening andextending into said recess into substantially overlapping spark-gaprelationship with said first mentioned electrode, adjacent portions ofthe respective electrodes being inclined with respect to each other andhaving their respective axes diverging within said recess toward saidcore to provide a tapered spark gap, the degree of the taper of said gapbeing so limited as to provide at the widest portion of said gap lessresistance to the spark than the resistance at the narrowest portion ofsaid gap when the difference in gas densities adjacent said respectiveportions is the greatest difference produced within the range ofconditions of engine operations ordinarily practiced in'the use of saidplug.

13. A spark plug comprising a shell having a chamber formed thereinadjacent one end portion thereof andhaving an opening in said endportion communicating with said chamber, an insulating core mounted insaid shell, an electrode mounted in said core and extending beyond theend thereof toward said opening, and a second electrode mounted on saidshell adjacent said opening and extending into said chamber intooverlapping spark gap relationship with'said first mentioned electrode,the mean axes of the respective electrodes being inclined with respectto each other and diverging from adjacent said opening toward said coreto provide within said chamber a tapered spark gap.

14. A spark plug comprising a shell having a chamber formed thereinadjacent one end thereof and having an opening communicating with saidchamber, an insulating core mounted in said shell, an electrode mountedin said core and extending beyond the end thereof and into said chamber,and a second electrode mounted on said shell and extending into saidchamber into operative relationship with said first mentioned electrode,the respective mean axes of adjacent portions of the respectiveelectrodes being inclined with respect to each other and divergingtoward said core to provide within said chamber a plurality ct-operative spark paths of varying lengths, one of said paths withinsaid chamber being approximately .007. of an inch longer than sulatorsecured to said shell and in part constituting a portion of the innerwall of said chambit iii)

arrears ber, an insulated electrode carried by said insulator andprojecting into said chamber, inner electrode means carried by saidshell and forming in cooperation with said insulated electrode arelatively long spark path having a, predetermined length and having aposition within said chamber predetermined with relation to saidopening, and means carried by said shell and forming a second spark pathhaving a relatively substantially smaller length .and being positionedrelatively substantially nearer to said opening, each of said sparkpaths being a substantially unidirectional lineal path ending at apredetermined side oi said insulated electrode.

16. In a spark plug and in combination a shell having within one oi! itsends a chamber having a constricted opening communicating therewith, aninsulator having a portion secured within said shell, an insulatedelectrode carried by said insulator and exposed within said chamber,electrode means supported by said shell and co-operatively associatedwith said insulated electrode to form within said chamber a relativelylong spark gap or spark path relatively near said insulator andelectrode means carried by said shell and forming in cooperation withsaid insulated electrode a relatively short spark gap or spark pathpositioned relatively substantially remote from said long spark path andrelatively n'ear said opening, each of saidspark paths being asubstantially unidirectional lineal path ending at a relativelypredetermined side of said insuiated electrode.

17. In a spark plug and in combination a shell having within one oi itsends a chamber havin an opening communicating therewith, an insulatorsecured to said shell, said insulator having a, portion thereofextending coaxially into said chamber toward said opening, an insulatedelectrode carried by said insulator and extending a substantial distancebeyond said portion thereof and into said chamber, inner electrode meanssupported by said shell and operativelyopposed in spaced relation to aportion of said insulated electrode relatively near said insulator toform at a predetermined side of said insulated electrode Bil dil

tilt

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and within said chamber a unidirectionalinner spark ,path oipredeterminedlength, electrode means supported by said shell andoperatively opposed in spaced relation to a portion oi said insulatedelectrode relatively remote from said insulator and substantially remotefrom said in= ner spark path and i'orming a spark path oi relativelyshorter length.

it. In a spark plug and in combination a metal shell having within oneoi its ends a chamber having an opening having a minimum transversedimension substantially smaller than the maximum transverse dimension ofsaid chamber measured from inner wall to inner wall of said shell andtree-ended wire-like electrodes having substantial portions thereofspaced away at all sides thereof from each other and from all said othermembers, said electrodes being cooperatively opposed within said chamberand providing within said chamber a plurality of substantiallyunidirectional operative spark paths of substantially varying lengthsand of varying positions with relation to each other.

19. In a spark plug and in combination a metal shell having within oneoi its ends a chamber having an opening having a minimum transversedimension substantially smaller than the mani= mum transverse dimensionof said chamber measured from inner wall to inner wall of said shell andwire-like electrodes cooperatively opposed within said chamber andwithin a predetermined side thereof and providing within said side ofsaid chamber a plurality of substantially lineal spark paths ofsubstantially varying lengths and oi substantially varying positionswith relation to each other, all other sides of said chamber being freeof obstructions to the admission and dischargaof gas to and from theinnermost portions of said chamber.

'20. In a spark plug and in combination a shell having within one of itsends a chamber having an opening, an insulator secured to said shell,cooperatively opposed electrodes supported respectively by said shelland by said insulator, one

of said electrodes being disposed throughout its 7 length substantiallycoaxially with said shell, and providing within said chamber andrelatively adjacent a predetermined side thereof a relatively long sparkpath relatively remote from said opening and providing a relativelyshort spark path positioned a substantial distance away from said longspark path in the direction of said opening.

21. In a spark plug and in combination a shell having a chamber formedwithin. one of its end, said chamber having an opening adjacent saidend, an insulator secured to said shell and constituting a portion ofthe inner wall of said chamber, an insulated electrode carried by saidinsulator and projecting into said chamber, a second electrode attachedto said shell and projecting into said chamber into substantiallyoverlapping electrically operative unequally spaced unilaterallydisposed non-parallel relationship with said insulated electrode,providing a spark gap of varying width within said chamber and betweensaid electrodes, the widest portion oi said spark gap beingsubstantially nearer said insulator than the narrowest portion of saidspark gap.

22. In a spark plug and in combination a shell having a chamber formedwithin one of its ends, said chamber having an opening adjacent saidend, an insulator secured to said shell and constituting a portion 01the inner wall of said chamber, an insulated electrode carried by saidinsulator and projecting into said chamber, electrode means carried bysaid shell and forming in cooperation with said insulated electrode asubstantially unidirectional inner spark path oi a predetermined linealdimension and having a predetermined position within said chamber andextending from adjacent said insulator toward a predetermined side ofsaid chamber and electrode means forming in cooperation with saidinsulated electrode a second spark path having a relatively smallerdimension and being positioned a substantial distance away from saidinner spark path, in the direction oi said opening.

23. The method of igniting fuel in a cylinder oi an internal combustionengine and in a chamber of a spark plug operatively related theretohaving an opening communicating with said cyiin= der, which method.consists oi admitting a portion of each charge of explosive gas from thecylinder into said chamber and producing a sparlr across a gap adjacentsaid opening when start= ing said engine and while said engine isrelatively low in temperature and is operating at rel. tively low speedand under relatively low load, and thereafter producing a sparkthroughout a path maintained substantially at a predetermined positionsubstantially within said chamber and relatively substantially remotefrom said opening and cylinder when said engine is relatively high intemperature and is operating at relatively high speed and underrelatively high load.

24. The method of igniting fuel in a cylinder of an internal combustionengine and in a chamber of a spark plug operatively related thereto andhaving a constrictedjopening communicating with said cylinder,which-methodconsists of admitting a portion of each charge of explosivegas from the cylinder into said chamber and producing a spark across agap adjacent said -of an internal combustion engine and in a chamber ofa spark plug operatively related thereto and having an openingcommunicating with said cylinder, which method consists of admitting aportion of each charge of explosive gas from the cylinder into saidchamber and producing a spark across a gap adjacent said opening whenstarting said engine and while said engine is relatively low intemperature and is operating at relatively low speed and underrelatively low load, and thereafter producing a'relativcly longer sparkthroughout a path ofv predetermined length and of predeterminedpositionwithin said chamber and relatively substantially remote from saidopening and cylinder when said engine is relatively high in temperatureand is operating at relatively high speed and under relatively igh load,and of'causing said charge of gas in said cylinder under said relativelyhigh conditions to be ignited by an advance of flame through saidopening and into said cylinder.

26. The method of igniting fuel in the cylinder of an internalcombustion engine and in a chamber of a spark plug operatively relatedthereto and having a constricted opening communicating with saidcylinder, which method consists of operating conditions.

admitting a-portion of each charge of explosive gas from the cylinderinto said chamber and of producing a spark across a gap adjacent saidopening when starting the said engine and while said engine isrelatively low in temperature andv is operating at relatively low speedand under relatively low load, and thereafter producing arelatively'longer spark throughout a path of predeterminedlength and ofpredetermined position within said chamber and remote from the inner.

walls of said chamber and relatively substantially remote from saidopening and cylinder when said engine is relatively high in temperatureand is operating at relatively high speed and under relatively highload, and of causing said charge of; gas in said cylinder under saidrelatively high conditions to be ignited by an advance of flame throughsaid opening and into said cylinder.

27. A method of energizing an internal combustion gasoline engine ofconventional type hav-;

ing a fuel compression cylinder, said method consisting of compressingwithin said cylinder successive charges of explosive gas and ofadmitting, into a chamber adjacent said cylinder and communicatingtherewith through an opening there.

between, a portion of each such charge and of igniting such charge byproducinga spark at one or anotherof two predetermined positions. one ofsaid positions being substantially remote from said opening andsubstantially within said chamber and the other of said positions beingsubstantially remote from said one position and spaced therefrom in thedirection of said cylinder, and of producing said spark selectively atone or another of said positions and in timing with the: compression ofan individual such charge and according to the value of coincidentaldifferentials in the density of said gas at said respective positions.

28. In a spark plug of the kind described and.

in combination, a shell having within one of its ends a chamber havingan opening communicating therewith, electrodes supported by said shellfrom each other, one of said pathsrbeing positioned within said chamber,said spark paths being automatically alternately operative selectivelyaccording to diiferentials in respectively 'adjacent EARL E. BIDWELL.

' and positioned to form a plurality of electrically parallel sparkpaths spaced a substantial distance.-

